sammyb123 - 6 months ago 36

Javascript Question

Not sure what is wrong here but I am trying to add a set of numbers in an array (not the whole array) but it looks like it is summing up the whole array:

`function sumPrimes(num) {`

var arr = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97];

var total = 0;

var index;

//loop through the whole array

for (var i = 0; i < arr.length; i++) {

//find matching prime number

if (num < arr[i]) {

// get index of prime number in the array

index = arr.indexOf(arr[i]);

//sum up total of prime numbers up to 'num'

for (var b = 0; b < index; b++) {

total = total + arr[index];

}

}

}

return total;

}

sumPrimes(10);

Answer

If your goal is to **calculate the sum of all prime numbers less than the given number**, then the solution is much easier.

Either

```
function sumPrimes(num) {
var arr = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97];
var total = 0;
for (var x of arr) {
if (x < num)
total += x;
else
break;
}
return total;
}
```

which works when **arr** is sorted, or

```
function sumPrimes(num) {
var arr = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97];
var total = 0;
arr.forEach(function(x) {
if (x < num)
total += x;
}, this);
return total;
}
```

that would work for an unsorted array as well.